The present invention relates to semiconductor devices and a method for making them.
A personal computer""s microprocessor may operate at a substantially lower voltage than the voltage at which the memory controller operates. In such a system, when signals are transmitted between the microprocessor and the memory controller, the input nodes of the microprocessor may be exposed to the higher voltage and the output nodes may be required to support that higher voltage. In addition, the output nodes may be required to source relatively high currents, when signals are to be transmitted from the microprocessor to the bus.
Certain features are currently added to a microprocessor, when it will be exposed to such voltages and when it must source such currents. To protect the microprocessor, when exposed to relatively high voltages, the microprocessor must include special circuitry. In essence, such special circuitry steps the voltage applied to the microprocessor""s input nodes down to the microprocessor""s operating voltage. To enable the output nodes to provide high currents, those nodes generally comprise wide devices. Adding such design features to the device requires setting aside relatively large chip areas, which are used for those purposes, and requires a relatively complex circuit design. Eliminating such features, which reduces die size and simplifies circuit design, is desirable.
Accordingly, there is a need for a semiconductor device that can tolerate high voltages and is capable of outputting relatively large currents. There is a need for such a device that does not require wide devices to generate high output currents or complex circuitry to protect it from high voltages. The MOS transistor of the present invention enables the production of such a device.
The present invention covers an MOS transistor that includes a gate electrode, a source and a drain. The source and the drain have a first conductivity type and are separated from each other by a first region having a second conductivity type that is opposite to the first conductivity type. A second region, which also has the second conductivity type, is formed adjacent to the drain and is separated from the first region by the drain. The present invention also covers a method for making such an MOS transistor.